Flat vs Reducing Interest Rates in Singapore

Two lenders in Singapore can quote the same percentage on the same loan amount and the same term, and charge wildly different totals — because one is quoting a flat rate and the other a reducing-balance rate. Singapore car loans are often advertised using a flat interest rate; personal instalment loans and mortgages are typically charged on a reducing balance. A flat rate and a reducing-balance rate are not directly comparable at the same percentage. This guide shows why, and how to compare quotes honestly using the effective interest rate.

How each convention computes interest

A reducing-balance rate (monthly rest) charges interest each month on the money you actually still owe. As you repay principal, the interest charge shrinks. A flat rate charges interest on the original financed amount for the entire term, regardless of how much you have already handed back. Take an illustrative S$90,000 car loan over 5 years. At a flat 4%: interest is 90,000 × 0.04 × 5 = S$18,000, so the instalment is (90,000 + 18,000) / 60 = S$1,800.00 a month. At the same 4% on a reducing balance, the amortising instalment is about S$1,657 a month and total interest is about S$9,450 — roughly half the flat-rate cost at the identical headline number. The car loan calculator reproduces both figures side by side; set the Rate Type selector to match whichever quote you are holding.

The effective interest rate: one honest yardstick

The effective interest rate (EIR) is the reducing-balance rate that would produce the same total cost as the offer in front of you. Because the flat structure charges interest on money you have already repaid, its EIR is always well above its headline number. The illustrative flat 4% over 5 years above works out to an EIR of about 7.68% — nearly double the advertised figure, and computed monthly. Singapore's financial regulators and the national MoneySENSE programme encourage borrowers to compare EIRs rather than headline rates precisely because the advertised percentage depends on the convention the lender chose. Lenders quote a mix of structures; check the rate type and the Effective Interest Rate your lender discloses before comparing any two offers.

One subtlety worth knowing: the EIR multiple grows as the term shortens. A flat rate over 3 years converts to a higher EIR multiple than the same flat rate over 5 years, because the principal is being repaid even faster relative to the interest charged. This is why you should never judge a flat-rate quote by its headline number alone — always convert, or let a calculator convert it for you.

A worked comparison you can check yourself

Suppose one finance company quotes the illustrative S$90,000 over 5 years at a flat 2.8%, and a bank quotes the same amount and term at 5.5% reducing balance. The flat quote sounds dramatically cheaper — but it is not. Flat 2.8% means interest of 90,000 × 0.028 × 5 = S$12,600, an instalment of S$1,710.00, and an EIR of roughly 5.3% — which is actually a whisker cheaper than the 5.5% reducing quote, not the bargain the headline suggested. Shrink the flat rate to 2.5% and the picture flips the other way. The arithmetic is not intuitive; run every real quote through the calculator's flat and reducing modes, compare the EIRs and the total interest, and only then decide.

The same discipline applies outside car finance. Instalment plans on retail purchases, renovation loans and education loans may all be quoted flat. Wherever the paperwork says "flat rate", translate it to an EIR before comparing it with any reducing-balance product — including the personal loan or mortgage offers you may be weighing it against.

What the rate does not tell you

No rate convention captures everything. Fees — processing fees, early-settlement administration, late charges — sit outside the headline and the EIR alike, and a longer term reduces the monthly instalment while increasing total interest at any convention. The Moneylenders Act separately caps licensed moneylenders at 4% per month on the principal outstanding, with late interest capped at the same 4% per month on the amount overdue and late fees capped at S$60 a month — statutory ceilings, not typical pricing, and a signal of what to avoid at the unregulated fringe. The honest comparison set is therefore: rate type, EIR, total repayment at the same term, and the fee schedule — each of which the calculators help you assemble. For the mechanics behind these numbers, read the companion guide on how loan repayments work in Singapore.